2001 Ford explorer sport trak pickup rear lights

I cannot figure out why all my lights work except for my driverside rear signal and break light. does anyone have any suggestions what i can do. I already tried changing the bulb but that did not work. thank you.

Going to take some work with a multimeter and a wiring schematic. First thing to check would be the ground(s); they're often the problem with lighting issues. Check autozone.com's repair info section for a wiring diagram.